Detect potential file enumeration activity ASIM Web Session

// HTTP response status codes indicate whether a specific HTTP request has been successfully completed.
// Please refer this for more details: https://developer.mozilla.org/en-US/docs/Web/HTTP/Status
let HTTPErrorCode=dynamic(["404"]);
let threshold = 10; // You can update this threshold to the value that suites your environment
// let FileNotFoundRequests = 
_Im_WebSession (starttime=ago(1h))
| where EventResultDetails in~ (HTTPErrorCode)
// Filter the logs to include only HTTP GET requests with an HTTP status code of 404 and '/' in the URL
| where HttpRequestMethod =~ "GET" and Url contains "/"
| summarize
    RequestCount = count(),
    FileCount=dcount(Url),
    EventStartTime=min(TimeGenerated),
    EventEndTime=max(TimeGenerated),
    RequestURLs = make_set(Url, 100),
    DestinationIPList=make_set(DstIpAddr, 100)
    by SrcIpAddr, SrcUsername, SrcHostname, DstHostname
| where RequestCount > threshold  // Adjust the threshold as per your requirements
| extend Name = iif(SrcUsername contains "@", tostring(split(SrcUsername,'@',0)[0]),SrcUsername), UPNSuffix = iif(SrcUsername contains "@",tostring(split(SrcUsername,'@',1)[0]),"")

status: Available
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Web Session Essentials/Analytic Rules/PotentionalFileEnumeration.yaml
version: 1.0.0
queryPeriod: 1h
query: |
  // HTTP response status codes indicate whether a specific HTTP request has been successfully completed.
  // Please refer this for more details: https://developer.mozilla.org/en-US/docs/Web/HTTP/Status
  let HTTPErrorCode=dynamic(["404"]);
  let threshold = 10; // You can update this threshold to the value that suites your environment
  // let FileNotFoundRequests = 
  _Im_WebSession (starttime=ago(1h))
  | where EventResultDetails in~ (HTTPErrorCode)
  // Filter the logs to include only HTTP GET requests with an HTTP status code of 404 and '/' in the URL
  | where HttpRequestMethod =~ "GET" and Url contains "/"
  | summarize
      RequestCount = count(),
      FileCount=dcount(Url),
      EventStartTime=min(TimeGenerated),
      EventEndTime=max(TimeGenerated),
      RequestURLs = make_set(Url, 100),
      DestinationIPList=make_set(DstIpAddr, 100)
      by SrcIpAddr, SrcUsername, SrcHostname, DstHostname
  | where RequestCount > threshold  // Adjust the threshold as per your requirements
  | extend Name = iif(SrcUsername contains "@", tostring(split(SrcUsername,'@',0)[0]),SrcUsername), UPNSuffix = iif(SrcUsername contains "@",tostring(split(SrcUsername,'@',1)[0]),"")  
kind: Scheduled
name: Detect potential file enumeration activity (ASIM Web Session)
triggerOperator: gt
severity: Medium
eventGroupingSettings:
  aggregationKind: AlertPerResult
id: b3731ce1-1f04-47c4-95c2-9827408c4375
triggerThreshold: 0
tags:
- Schema: WebSession
  SchemaVersion: 0.2.6
queryFrequency: 1h
alertDetailsOverride:
  alertDescriptionFormat: User generated multiple requests '{{RequestCount}}' that has resulted in error code '404', suggesting the possibility of file enumeration activity. It's important to investigate the source and patterns of these extensive 404 errors to identify potential security threats. Details about this error code could be found [here](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status)
  alertDisplayNameFormat: User '{{SrcUsername}}' with IP '{{SrcIpAddr}}' has been observed with performing file enumeration activity
description: |
    'This detection method identifies potential cases of file enumeration activity. The query is designed to identify client sources that generate multiple requests resulting in 404 error codes'
requiredDataConnectors: []
customDetails:
  RequestCount: RequestCount
  RequestURLs: RequestURLs
  DestinationIPList: DestinationIPList
  FileCount: FileCount
  EventStartTime: EventStartTime
  EventEndTime: EventEndTime
relevantTechniques:
- T1083
- T1071
- T1110
tactics:
- Discovery
- CommandAndControl
- CredentialAccess
entityMappings:
- entityType: IP
  fieldMappings:
  - identifier: Address
    columnName: SrcIpAddr
- entityType: Account
  fieldMappings:
  - identifier: Name
    columnName: Name
  - identifier: UPNSuffix
    columnName: UPNSuffix
- entityType: Host
  fieldMappings:
  - identifier: HostName
    columnName: DstHostname
- entityType: Host
  fieldMappings:
  - identifier: HostName
    columnName: SrcHostname